Amanda Knox has flown back to her U.S. home city of Seattle, after serving four years in prison in Italy on murder charges.

Knox, 24, burst into tears on October 4 in a brief media appearance at the airport in Seattle, saying she was "overwhelmed" at returning to the United States.

Knox and her Italian ex-boyfriend Raffaele Sollecito were acquitted on October 3 by an appeals court in Perugia in central Italy of the 2007 sexual assault and murder of British student Meredith Kercher.

"I'm really overwhelmed right now," Knox told reporters upon arriving in Seattle. "I was looking down from the airplane and it seemed like everything wasn't real. What's important for me to say is just thank you to everyone who has believed in me, who has defended me, who has supported my family."

Knox and Sollecito had been convicted of the crime in 2009, but had maintained their innocence in a case that was closely covered by news organizations in the United States, Italy, Britain and other countries.

A break in the case occurred when independent forensic experts challenged the integrity of the scientific evidence that police collected in the original investigation that led to the conviction of Knox and Sollecito.

Rudy Guede, from the Ivory Coast, is currently serving a 16-year prison sentence in Italy after being convicted of Kercher's murder in a separate trial.